Ferromagnetic Resonance Modes in Single-Crystal YIG Films

The availability of narrow-linewidth single-crystal yttrium iron garnet (YIG) films1 allows the detailed observation of a large number of ferromagnetic normal modes in a given sample for a range of sample sizes and shapes which covers the exchange-dominated through the magnetostatic limit. The absorption spectra of circular disks from 0.4- to 9-μm thick with aspect ratios from 22 to 1400 have been measured and explained theoretically. We report for the first time a spectrum having the ⊥ resonance frequencies of all higher-order modes well above that of the main resonance. In a 0.4-μm-thick, 3×10−3-in.-diam disk, the closest mode is 10 Oe away from the main resonance. In the thickest and in the thinnest samples, the magnetostatic and exchange modes were well separated. In the intermediate thickness range from 1 to 4 μm, modes having comparable magnetostatic and exchange energies were observed, making the spectrum more complicated. The intensities and frequencies indicate that the spins are pinned at the small edges of the film and that in very thin films (less than ≈3 μm) the low-order modes are pinned1 by a Portis-type well for which the variation of the internal field across the sample thickness is not purely parabolic, while unpinned modes have been reported in a 12.4-μm-thick sample.1